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Re: [T3] fuel pump relay failure?

On 14 Oct 2004 at 15:38, C.Rochambeau wrote:

> > On a manual tranny '70 there are 2 red wires going to the relay (in addition to 
> > the 2 in the plastic plug), but there are 3 terminals on the relay.

> The fuel pump relays in both our cars have 5 leads. The blue/yellow
> and grey, which were both in the plastic casing before I freed them to
> fit the newer production Bosch relay [test subject from my car]. The
> heavier gauge [unless that is my imagination] red lead that supplies
> voltage all the time, and then 2 more red leads that share the common
> connection. At least this is how I set about hooking it up; does that
> sound correct or could it be contributing to the problem? That layout
> functions correctly on my car.. The wires in his were there already
> [and hooked up in the same manner], though now to think of it, I
> didn't bother to glance at the VIN, so 1970 is on the sellers word.. 

There is one red wire that comes from the fuse box; that's the hot supply wire.

There is one red wire that joins up with a brown wire and heads forwards to the 
fuel pump.

In some years there is a 3rd red wire that is part of the wiring harness and 
heads back to the engine compartment. It is only used on AT cars; on MT cars it 
is cut off back there. You can see it if you look next to the wire that leads 
to the oil pressure switch. I thought this usually was cut off in front, too, 
but I may be wrong about that.

In your case I would start by just connecting the supply and pump wire, and 
then checking to see if the relay turns the pump on and off. If it doesn't, 
then you may have your wires on the wrong pins.

BTW, these relays very seldom go bad, and when they do you can usually bring 
them back by just opening them up and cleaning up the contacts.

> While we were troubleshooting the car from a 'dead, will not start, and no pump' state, 
> you could hear the first click, at which point the pump should have started, but the 
> second click was nonexistent. Once in the key on state, we stuck a jumper from pin 30 to 
> 87 of the fuel pump relay and that got the car home.

You should start by checking to see if you get voltage between the two coil 
wires (the ones in the plastic connector) for ~1 second when you turn the key 
ON. If you do, but the relay doesn't respond, then there is a problem with the 
relay. If there is no voltage there, then there is most likely a wiring problem 
leading to the relay.

> Does that sound like relays, or are we fishing for red herrings?

Given what you've told us, I don't think this is a relay problem.

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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